1. Field Of The Invention
This invention relates to pressure responsive well tools, and more particularly to a pressure responsive safety valve.
2. Description Of The Prior Art
In both drilling and production operations, conditions sometimes occur which make it necessary to quickly close the drill string tubing or production tubing in order to shut off flow of fluid from the formation.
Tubing string valves for use in drilling, testing and producing wells are well known.
Such valves are often constructed to be responsive to changes in well annulus pressure. Two examples of such annulus pressure responsive valves are U.S. Pat. Nos. 4,064,937 to Barrington and U.S. Pat. No. 4,063,593 to Jessup, both assigned to the assignee of the present invention. In both of these references, the well annulus pressure is applied to one side of a power piston defined on an actuating mandrel, and the other side of the power piston is in communication with a sealed low pressure zone.
Another manner of operating such a device is shown in U.S. Pat. No. 3,814,181 to Young which discloses a safety valve which utilizes the ambient well annulus pressure, rather than an artificial change in well annulus pressure, to operate a safety valve in response to sensed changes in pressure within the production tubing.
Also, other safety valves have been designed to be operated by artificially imposed changes in pressure within the production tubing, such as seen for example in U.S. Pat. No. 3,850,238 to Hill.